Add hostname to bucket name

[Terrance]

The built-in ActivityWatch bucket names are suffixed with the local machine's name (e.g. aw-watcher-window_HOSTNAME). AW recently shipped support for syncing data between multiple devices (aw-sync), which works without conflicts due to the uniquely-named buckets.

This plugin however does not suffix its bucket name, aw-watcher-tmux, which will likely cause problems when trying to sync between two machines both using the plugin.